The field of radio frequency identification (“RFID”) devices has shown that it is possible to exchange data with UHF or microwave devices, e.g. an RFID tag, that have little or no on-board power supply. RFID tags are often used to track inventory and to determine the location of objects. For example, a department store may place an RFID tag on a piece of clothing. An RFID interrogator may be placed at the entrance and/or exit of the department store. If the RFID tag indicates that the clothing has not been purchased, upon interrogation by the RFID interrogator, an alarm may sound when the article of clothing passes by the interrogator, thus helping to reduce theft.
There are two types of RFID tags: passive and active. An active RFID tag has an on-board power supply and transmits data stored on the tag to a receiving station. These types of tags are typically used when a local power supply is available and, because these tags are typically more expensive than passive RFID tags, when cost of each tag is not the primary factor. Passive RFID tags may or may not have an onboard power supply. The primary difference between the active and passive RFID tag is that the passive RFID tag employs backscatter signal modulation to reflect back a data signal when interrogated by an RFID interrogator, whereas the active RFID tag transmits according to preprogrammed schema and uses an RF transmission chain to create and send its data signal. The active RFID tag may also be configured to transmit a data signal when interrogated.